There are three major objectives of the proposed research, much of which will be effected by means of a differential orthograde labeling strategy. This strategy combines autoradiographic and degeneration tracing methods so that the terminals of two different pathways can be labeled simultaneously in the same preparation. The remainder will be effected by using a triple labeling procedure in which retrograde labeling methods (horseradish peroxidase) are added to the differential orthograde labeling procedure. The first objective of the research is to continue to study the patterns of convergence and divergence of various afferent inputs to the cat thalamus (and inferior olive) using the orthograde differential labeling strategy. The studies will involve comparisons of input to the thalamus (and inferior olive) from various electrophysiologically identified portions of the somatosensory and motor regions of the cerebral cortex and from the reticular formation and the central gray. When complete, it is proposed that a major review article be written containing an analysis of the anatomical studies on the thalamus in their physiological, behavioral and clinical contexts. The second objective is to use the triple labeling strategy to study the relationship between the afferent inputs to various regions of the cat thalamus (and inferior olive) and the subsequent efferent projections of these regions to the cerebral (and cerebellar) cortex. One such study will compare the thalamic location of spino-thalamic and cerebellar terminals to the thalamic location of the cells of origin for terminals in area 3a of the cerebral cortex. The third objective is to repeat in monkeys the experiments that were done earlier in the cat on the thalamic projections from the dorsal column nuclei, the spinothalamic tract and the cerebellum.